Laboratory circulating evaporator



Feb. 8, 1949. 1 L 2,461,389

LABORATORY CIRCULATING EVAPORATOR Filed Feb. 23, 1945 no no 10 10 um IN VEN TOR.

Patented Feb. 8, 1949 U N Y!" ED STAT E S FlfCQE.

LABORATORY CIRCULATING EVAPGRATOE David; 1;. Mitchellg. Decatur, 111,.

Application Fcbruary 23, 1945 Serial No. '-l'9",44 3

1 Claim. 1.

This invention relates. to. improvements in laboratory evaporatorsin which the liquid or solution being evaporated is continuously circulatedfirst' through a heat exchanger and: second through a chamber that permitsseparation of vapor from: liquid; More specifically; it relates' to improvements in-such laboratory evaporators that are designed to operate under reduced pressure, and whose surfaces in contact with the liquid being evaporated consist of glass or similar thermoplastic chemically resistant material.

The objects of this invention are to provide an evaporator that, one, is'simple compact-and efficient, two, reduces entrainment duetofoaming; spraying, and other causes, three, practically eliminates explosive ebulliti'on due to superheating of liquid, four, prevents-crusting of-sol'id's that separate from solution during the evaporation and consequent damage to those solid'sir they: are sensitive to heat, five; is: easily: charged and dis.- charged', six, can be cleaned without being disassembled, and seven, is easily assembled and disassembled.

The foregoing objects are attained bymeansof an improved evaporator illustrated in the accompanying drawing in which:

Figure 1 is perspective view of the entire evaporator with a cut-away section of the-heat exchanger jacket. Suc'haccessories as supports, condenser, condensatereceiver, vacuum pump, and lines for conveying heating fluid to andfrom the heat exchangerare not shown.

Figure 2 isa vertical section of the heat exchanger tube assembly.

Figure 3 is a horizontal section of the vapor separator along the line 24--24 -of"Figure 1.

To operate the evaporator; vacuum: is applied to tube l5 and liquid is drawn into the apparatus through tube 5'- ancl open valve fi unt'il vapor chamber l is about one-half fun of: liquid; at

which point valve 6- is clo'sedi Ifii'quiti now fills liquor return tubes f, 3 4 and allor the heat exchanger tube assembly 'l'9l ll'--l ll--llllil 2 to the samelevel as it is in chamber I l he applied vacuum is allowed to reach a maximum, or it is brought to some predetermined value if a pressure regulator, not shown, i'susedi Steam is then admitted t-hroughtube l8 to the inside of the heat exchanger jacket 11 and exhausted; with condensate and excess steam, through tube it; If hotwater' or other heating liquid is used, it. can, if desired, beadmittedthrough tube l ii and. discharged through tube Hi so -as to provide a flow that is parallel to the'flow' ofliquid inside the heat exchanger tubes l 010"-Hl": Noposlin chamber i and in tube extensionst2 and 3% (Simulation, down through tube extensionseivrmd' trumi' up throughv heat exchangeirtuhe assemhly, continues sorlbng as there-is. sufficient head of liquidin chamber 1 and tubeextensions: 2 and to support a column of mixedi vapor and liquid extending highenough in. tube to; overflow into; chamber I. l 5= andmasrabe disposed: of 'in'v various: ways. It may" be condemned on a. cold solid surface, or in a cool liquid, or it-may' beled directly'toa steam jet aspirator or to avacuum. pump that. will handle uncondensedvapor;v

rlldditi'onal liqui'd can be admitted to the systern through valve 6; intermittently orcontinueously as desired, to compensate for materialzramoved asvapor; Thisaddition can be continued until increasing viscosity ofthe-concentrated? solution or accumulation of precipitated; solids. in.- terferes with circulation. Continuous. evaporattion of a dilute solution to a given concentration can also-be conducted with: this evaporator; To do this, the charge in the evaporator is first brought to the desired; concentration, then. some oftne charge. is drawn off continuously under vacuumthrough a F-connection in return tube a (not shown) while f-reshdilute solution is fed incontinuously through inlet tube 52. Rates of feed and withdrawal of concentrated solution must be-ad justed to the capacityot the-evapora- Vapor passes offi throughtuhe Such adhering material is easily flushed out by closing valve 6, renewing the vacuum, slowly washing operation, which uses a volume of water that is quite small in proportion to the volume of a full charge, can be repeated as often as required.

Aside from the heat exchanger jacket I! and its associated parts, the evaporator consists of only three integral parts connected together with air-tight connectors 292I22. These connectors may be rubber sleeves, such as short sections of appropriate size rubber tubing, in which case the ends of the connected tubes are butted closely together, or they may consist of ground glass joints, preferably the standard ball and socket type. This construction permits rapid assembly and disassembly of the apparatus. The three integral parts of the evaporator referred to above are, one, the vapor separator consisting of chamber l and rigidly connected tubes 2, l5, and l3'-i 4, two, the combined liquid return and inletoutlet tube consisting of tube 4 with long bent arm 3 and attached valve or stopcock 6 and tube 5, and, three, the heat exchanger tube assembly consisting of inlet tube 1, manifold chamber 9, tubes [0-in-1 0, manifold chamber H and outlet tube l2.

Because of its ease of fabrication and resistance to attack by chemicals, glass is the preferred material of construction for those parts of the evaporator that'come into contact with the liquid being evaporated. Any other chemically resistant thermoplastic material, however, that can be worked like glass and has suflicient mechanical strength at 100 C. can be used in place of glass. "The heat exchanger jacket and it associated of'the flask with tube l5, blowing a hole in the bottom of the flask andsea'ling on tube 2, and lowing another hole inthe upper part of the flask and inserting combined tubes l3l 4. Tubes 13' and M are preferably joined and attached to the flask wall by means of a ring seal. methods of inserting combined tubes 13 and [4 maybe used, however. For example, if rubber in contact with the evaporated liquid can be tolerated,ithe ring seal can be replaced with a short flared glass nipple which will accommodate a rubberstopper bored to fit tube l3. In this case asingle tube properly bent can be used to convey the mixture of vapor "and liquid from tube l2 7 into chamber I. Y

The combined liquid return and inlet-outlet tube assembly, consisting-of bent tube-3 sealed to tube 4 whoseupper nd'joins with lower end of tube 1 and whose lower-end terminates invalve 6 and nipple 5, is conveniently prepared from standard glass tubing and a glass stopcock. 'If,

An integral all-glass heat exchanger, consisting of tube assembly and jacket can be Other again, contact of rubber with the liquid being evaporated can be tolerated, valve 6 may consist of a screw clamp on a short section of thick walled rubber tubing instead of a glass stopcock.

The heat exchanger tube assembly is conveniently made out of standard glass tubing and two round bottom flasks that are small with respect to chamber l. Holes are blown in the bottoms of the flasks and lengths of glass tubing are sealed thereon as illustrated in Figure 2. If the necks of the flasks, devoid of rim, are not long enough to project through the packing glands 8-46 on the ends of the heat exchanger jacket and provide proper connections with tubes 4 and i3, or if they are of improper diameter, they can be cut off and replaced with suitable lengths of proper sized glass tubing. Although only three heat exchanger tubes are illustrated in the drawing, more may be used if desired. Five 10 mm. outside diameter tubes can be easily arranged on the body of a ml. round bottom glass flask; one tube is centered on the bottom of the flask and the remaining four are spaced ninety degrees apart on a circle near the flasks equator. Still more tubes, arranged in one or more circles of attachment points, can be sealed to larger flasks.

. The heat exchanger jacket I! can be made as follows: A cylinder is made out of thin sheet metal or one is cut from metal tubing if tubing of proper s'me and appropriate Wall thickness is available- A sheet metal end plate 25 carrying a centered hole slightly larger than tube 7 is brazed flush with one end of the jacket. The gland body 8 of packing gland 8-3fl is then centered over the hole in end plate 25 and soldered to the plate. A sheet metal flange 26 carrying six bolt holes to accommodate bolts 23 spaced sixty degrees apart is soldered flush with the other end of jacket ll, Another sheet metal end plate 28 is cut to the same diameter as flange 26. Bolt holes corresponding to those in flange 26 are drilled in this plate, also a center hole slightly larger than tube I2. The gland body 16 of packing gland IS-29 is centered over the center hole in the plate and is then soldered in place. Holes providing a snug fit for tubes l8 and I9 are drilled near the ends of jacket H, and short metal nippics are inserted therein and soldered in place. The packing glands 8-30 and iii-29, and the gasket 26, which may be any compressible material that will withstand water and steam at 100 C., provide for steam and watertight connections around the heat exchanger tube assembly. One end plate of the jacket has to be removable in order to allow assembling and disassembling of the heat exchanger.

It is not essential to this invention that the heat exchanger jacket be constructed of metal. Any means for covering the heat exchanger tube assembly so that a heating fluid can be circulated over its outside surfaces will do. For example, a glass jacket similar to the jacket on laboratory straight tube condensers, with inlet and outlet tubes near its ends, can be attached to tubes 1 and I2 with ring seals. This provides a very satisfactory and compact heat exchanger, but requires considerable glass blowing skill in its construction.

The use of a metal heat exchanger jacket and packing glands, as illustrated in the drawing, precludes the convenient use of ground glass joints for connecting the heat exchanger to the other parts of the evaporator. This is so because the packing gland followers 29-30 will not slip over the expanded parts of the glass joint. Short joint nipples can be sealed to the tubes extending greased $1 pastithepackingglands after thejacket is as.- senihled; but this. unduly lengthens the heat. exchanger. Ground glass joints, especially the standard? ball and; socket. type, are conveniently and. advantageously used on the heat. exchanger w-heriit is; equipped with the foregoing described all glass jacket. A. ground glass joint: can be used toconnect: the vaporseparator with the liquid return tube. regardless of the construction. oi the heat exchanger jacket.

Kismet-essential that chambers 9iand Hi in theheatexchanger tube assembly be constructed. of round bottom glass. flasks, or that they be sphericaliim shape; They may, if it is so desired, consist of irregularly shaped large or small bulbs bination, aniinlet: tube with an. expanded chamberattached at one end, an outlet tube with a similar expanded chamber atone end, and a plurality of tubes. connectingthe two expanded chambers, and, three, that the assembly be constructed ofgl'assorsimil'ar chemically resistant thermoplastic material It. is: desirable, though not essential, that the inlet and. outlet: tubes be in about the samez'straight line with the connecting tubes parallel thereto.

Another important feature of this invention isthe design' of the vapor separator. it has previously been: proposed to convey the mixture of vapor" and liquid emerging form the heat exchanger-into the vapor. chamber i with a tube entering the upper: part of the chamber and sealed flushwith the.- cham'her'wall. When this is done, there occurs much; entrainment of liquid through. thezexit vapor tube t5, owing toprc-nounced creep ing offliquid along the chamber wall. between tubes l3: and 1'15. Although most of the entering mix ture of vapor and liquid plunges directly into the chamber, aconsiderable. proportion of: it fans out. along the chamber walllin all directionsfrom the: tube.- entrance. To overcome this difiiculty, it-has been suggested-that tube it: extend a short distance into the chamber, rather then stop flush with: the walla This reduces the: entrainment somewhatbut does notv eliminate itraltogether, because-the entering stream of liquid and vapor strikeslthe opposite'wallof the chamber-wlthconsiderableforce and: again splashes and: fans out:

pinge violently againsttlhe chamber wall and fan, out-asiit. didbefore. Instead; it; creates asmooth rapid 'wliirling. motion of the liquid and vapor in the chamber that eliminates all former entrainment. There: isv now no creeping or fanning; out of. liquid: along the chamber walls toward the exit vapor tube, and the whirling. motion of the vapor developswenough centrifugal force tozthrow' but". the finest droplets: of spray against. the

sid'essof the chamber where they drain down to the liquid; charge: below. Furthermore. the whirling motion. of the entering stream of vapor and licuid;. as: well as that of". the main charge of liquid in. the; chamber; breaks down but the most-5 peristent types of; foam that may develop during,

oust entrainment in: conve'ntionat laboratory evaporators; whether of the circulating or non circulating'type, are: immediately dispersedrirr the vaporseparatorof? my evaporation.

It-' is: not. essentiali that the vapor separato chamber I be:spherilcailiinxshape, or thattheyapor exist tube: I15; be centered; at. its top, or theliquid? retunr tube; 21 centered at: itsbottom', or? that. the: vapor-liquidninletrtube 1:3 enterwthe top part. of thevchamben. 'Illlbflsli and; [5: can be ofli center; tube 131 carr enter chamber I: midway between. its. top-rand bottom, or: evem at its lower porti'om. andsbottomof. chamber lcan be drawn out-to: a pear shape: if. desired. The vapor separator chambermay be; cylindrical in shape; The three; essentiat features oi'thea vapor: separator are; one; its-horizontal:crossrsection shalialoe essentially circular so as: not; to. impede the circular motiom the liquid: and. vapor therein, two, the extension; of they vapor liquidt'inlet tube inside theachamher shallbe. bent sideways: as shown in Figure" .2 so as: to initiate the desired. whirling motion: otithe: charge and; three, it shallbe constructed. of? glass or similar chemically resistant thermoplastic; mae

teria-L,

Still another ieaturesofi the invention is; the: de sign of combined bent: tube. and tuber: that serves both asga means for returning, liquid from: the: vapor'separator to.-the; heat. exchanger and-as; a means for charging and. dischargihgtthe evapoirator; Tubei t, whiclr isaa-stra-ight line extension; of tube 1,. the inlet tube for the: heat exchangertube assembly, permits admission ofafresh. liquid; to: the: evaporator while it, is bperatingrwithouti causing any of: the admitted liquor, to back into: the-vapor separator and. interrupt. circuiaztion. The upward sianting arm-. 01. tube: ii lfa cihitates drainage. Preferably the:acute;-ang;le--b.etween: tube and the slanting; armof tuberlrshouldi baforty fivedegrecs or less;

There-are norig-id, limitations on the sizes and lengths of. the: tubesaused to connect the vapor separator with the; heat exchanger anditol lead vaporvaway from the vapor separator. It-isz'adivisable, howevergthat the cross sectional area: of: the vapor outlet tube and of'the'tube leading: from the top of. the heat exchanger to thc vaporr separator be notv less than the: combined cross sectiona'h areaoftheheat exchanger tubeaotherwise: very high vapor'velocities, with accompany-' inggundesirable pressurepdrops, will occur.

Ifi unevenzebullition indicativeof: liquor super,- heating doesoccur irrthe: circulating: evaporator; it: canimmediately be eliminated by'admitting a smalt stream. of air bubbles intothe circulating, liquidiat a point below thezseat-i exchanger so: that. the bubbles rise through therheat exchanger'tube:

ortuhesa The following. directions and specificationsaas to dimensionsandimaterials of constructicrrrefer' to a specific: example of an evaporator conteme platedibyfthisinvention.

Heat exchanger tithe unit-Jive pieces: of" Pyrex glass tubing having. an outside diameter of 10 mm. and an. inside diameter of 8 mm; are sealed between thebottomsoftwo 1 00 ml. round 7 bottom. Pyrex glassflasks whose necks. have been. cut off. closet'o: the spherical bodies.

of Psrrex glass tubing having an inside diameter lcng, is sealed to theedges of appropriate'holesblown: inthe centersof the bottoms of the I00 m1;

The neckof" each fiaskisreplaced with a 4111011 length flasks. The other four tubes, about inches long, are sealed to the edges of appropriate holes blown at points 90 degrees apart on circles near the equators of the flask bodies. Entire length of the heat exchanger tube unit is about 32 inches.

Heaterchanger y'acket.--A rectangular piece of 16 gage copper sheet 24 inches long and 11 inches wide is rolled into a cylinder having an inside diameter of slightly more than 3 inches, and the abutting long edges are soldered together. A circular plate fitting snugly and flush within one end of the cylinder and carrying a centered hole one inch in diameter is cut from copper plate 0.25 inch thick and soldered in place. The gland body of a conventional packing gland adapted to receive the 22 mm. inch) outside diameter end tube of the heat exchanger tube assembly is centered over the hole in the foregoing jacket end plate and soldered in place. A circular flange with an outside diameter of 4.5 inches and an inside diameter such that the flange fits snugly over the other end of the jacket is cut from 0.25 inch thick copper plate, drilled to take six 1% inch bolts spaced 60 degrees apart on a 3.5 inch circle, and soldered flush with the end of the cylinder. Another end plate, 4.5 inches in diameter, is cut from the 0.25 inch thick copper plate. Both holes corresponding to those in the foregoing flange are drilled in it, also a center hole one inch in diameter. A gland body, adapted to receive the 4; inch outside diameter end tube of the heat exchanger tube assembly, is centered over the center hole in the larger end plate and soldered in place. One quarter inch holes are drilled one inch from the top of the jacket and 0.5 inch from the bottom, and over these are soldered 2 inch nipples of 0.25 inch copper tubing to serve as steam inlet and condensate outlet.

Vapor separator.'l2he neck of a standard short neck round bottom 5 liter Pyrex glass flask is out off close to the body of the flask. The remaining attached short section of neck is appropriately constricted, and to it is sealed an eight inch length of Pyrex glass tubing having an inside diameter of 21 mm. and an outside diameter of 25 mm. The attached tube is then given a gradual 90 degree bend to provide the vapor exit tube l5 shown in Figure 1. An appropriate hole is blown in the bottom of the flask, diametrically opposite the vapor outlet, and to it is sealed 2. 4 inch nipple of Pyrex glass tubing having an inside diameter of 18 mm, and an outside diameter of 22 mm. This provides tube 2, a part of the liquid return line, as shown in Figure 1. Another appropriate hole is blown in the flask at a point about 45 degrees from the top, as measured on a meridian, and through this hole is inserted a portion of a section of glass tubing about one foot in length having an inside diameter of 18 mm. and an outside diameter of 22 mm. This section of glass tubing is bent before insertion in such a manner that that portion inside the flask bends sideways and slightly downward as shown in Figures 1 and 3. The tube and flask are then fused together to make one integral part so that the tube forms one continuous open passage through the wallof the flask and into the flask. The portion of the tube attached to the outside of the flask is then bent downward in a gradual 90 degree curve starting a short distance away from the flask, so that the center line of the downward, pointing vertical portion measures about 7 inches from the vertical center line of the flask. All except about one inch of the straight vertical part of the downward pointing tube is then cut ofi. This provides tube !3 as shown in Figure 1. Combined liquid return and inlet-outlet tube: An appropriate hole is blown in the side and middle of a 6 inch straight length of Pyrex glass tubing of the same size as that'attached to the bottom of the vapor separator. To the edges of this hole, and at an angle of about 45 degrees with the 6 inch tube, there is sealed a 32 inch length of the same glass tubing. At a point on the longer tube about 10 inches from its attachment to the short tube, the tube is softened by heating and bent in a gradual curve so that the longer arm of the bent tube lies in the same plane with the 6 inch tube and parallels it at a center to center distance of about '7 inches;

Assembling the heat exchanger.-End tube 1 of the heat exchanger tube assembly is thrust into the open end of the heat exchanger jacket and through the hole in the far end plate 25 as far as it will readily go. The free larger end plate 28 carrying an annular rubber gasket 27 with matching bolt holes is then slipped over the tube at the opposite end of the tube assembly and bolted into place on the flanged end of the jacket, using short stove bolts. String packing is placed in the packing glands 8-16, and it is held in place by followers 2930 that make threaded connections with the gland bodies. The end tubes of the assembly extend about 1.5 inches beyond the packing glands.

Assembling the eeaporator.-The assembled heat exchanger is mounted in a vertical position on suitable supports by means of clamps afiixed to-the jacket. The lower end of the tube assembly preferably should lie 18 inches or more above the platform, table, or floor supporting the evaporator so that vessels can be manipulated beneath the evaporator inlet-outlet tube 5 whose lower end falls 6 inches below the lower end of the heat exchanger. The free end of the liquid-vapor inlet tube IS on the vapor separator is then attached to the upper end tube of the heat exchanger l2 by means of a 2 inch section of firmly fitting thick walled rubber tubing 22, and is held firmly in place in a vertical position by means of clamps attached to the vapor exit tube I5 and to the liquid return tube 2. The combined liquid return and inlet-outlet tube 3-4 is then put in place, as shown in Figure l, to test its fit. If it fits, connections are made with the vapor separator and heat exchanger using short sections of appropriate thick walled rubber tubing 2il2l. If it does not fit at first, alterations as to length of the long parallel arm and distance between the parallel arms are made until it does fit.

Havingthus decribed my invention, I claim:

A laboratory circulating evaporator of the class described comprising in combination: an integral heat exchanger tube assembly comprising two" manifold chambers, a plurality of tubes connecting said manifold chambers, an inlet tube connected to one manifold chamber, and an outlet tube connected to the other manifold chamber, said tube assembly providing for flow of the liquid being evaporated, and vapors thereof, on the inside of its tubes and manifold chambers; an integral vapor separator assembly comprising a chamber whose horizontal cross section is substantially circular, a vapor outlet tube connected to the top of said chamber, a liquid outlet tube connected to the bottom of said chamber, an inlet tube for mixed vapor and liquid connected to the chamber at a position between its top and through the wall of said chamber for a short distance and directed toward an adjacent part of the chamber wall, whereby the incoming stream of mixed vapor and liquid is delivered tangentially against the chamber wall and imparts a smooth whirling motion to the vapor and liquid within said chamber; an integral tube assembly that provides combined improved means for charging, discharging, and. washing the evaporator, and for returning liquid from the vapor separator assembly to the inlet tube of the heat exchanger tube assembly, said tube assembly comprising a straight tube with an opening in its wall, and a bent tube consisting of a bend and two substantially straight arms, the end of one of said arms being sealed to the rim of the opening in said straight tube so that said attached arm and said straight tube form an acute angle, the other of said arms lying in the same plane with said straight tube and being parallel thereto; means for heating the outer surface of said heat exchanger tube assembly; means for connecting the outlet tube of the heat exchanger tube assembly to the mixed vapor-liquid inlet tube of the vapor separator assembly; means for connecting the liquid outlet tube of the vapor separator assembly to the combined liquid-return charge-discharge tube assembly; and means for connecting said combined tube assembly to the inlet tube of the heat exchanger .tube assembly. I 7

DAVID T. MITCHELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

